Output window and coupler for high frequency electron discharge device



ER FOR H G Nov. 30, 1965 J. D. MILL 3,221,206

OUTPUT WINDOW AND COUPLER IGH FREQUENCY ELECTRON DISCHAR E DEVICE 2Sheets-Sheet 1 Filed Feb. 21, 1964 FIG. 4

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Nov. 30, 1965 Filed Feb. 21, 1964 FIG.6

FIG.8

United States Patent 3,221,206 OUTPUT WINDOW AND COUPLER FOR HIGHIgRgIOUENCY ELECTRON DISCHARGE DE- John D. Miller, MountainView,"Calif., assignor to Varian Associates, Palo Alto, Calif., acorporation of California Filed Feb. 21, 1964, Ser. No. 346,530 17-Claims. (Cl. 315--3.5)

This invention relates in general to the field of high frequencyelectromagnetic transmission and more particularly to high frequencyelectron discharge devices and electromagnetic energy transmission meanstherefore.

Present state of the art electron discharge devices are under continuousdevelopment with the trend of development being higher power, higherfrequency, Jbroader bandwidth, increased transmission efficiency andsimplification of overall design. Suchhigh frequency electron dischargedevices as the traveling wave tube, klystron and magnetron are typicalexamples of theaforementioned devices which are presently undergoingextensive investigation with the intention of improving theaforementioned characteristics thereof. One of the major stumblingblocks in attempting to build an improved high frequency electrondischarge device of the aforementioned types is the electromagnetic waveenergy couplers utilized to transfer electromagnetic energy both to andfrom the device through differential vacuum conditions and dilferentialimpedance conditions. In particular with the advent of higher powersserious problems are encountered by the tube designer in providingadequate means for transmission of the electromagnetic wave energy fromthese devices without appreciable sacrifices in bandwidth and efficiencyof transmission. Furthermore, at high power levels electrical breakdownphenomena and overheating of the transmission device couplers, inparticular the electromagnetic wave permeable window portions of saidcouplers and the presence of spurious modes, vhereinafter termed ghostmodes, in said window portions, present a formidable array of problemswhich must be considered and overcome.

In addition to the aforementioned design problems, the ever presentnecessity of minimizing cost and attempting to simplify and generalizethe design to provide a solution to a wide variety of conditions must bedealt with.

The present invention provides what is considered a novel solution tothe aforementioned design criteria which results in improved highfrequency electron discharge devices of the aforementioned types andwhich further results in a noveltransmission coupler for high frequencyelectromagnetic energy.

The present invention provides the aforementioned solution in thefollowing manner. Starting with the basic conditions of providing highfrequency electromagnetic transmission coupler means between two pointswhich are characterized by having differential vacuum and differentialimpedance characteristics itherebetween, the problem involvestransferring electromagnetic energy between said points, whileattemptingto minimize loss of energy, narrowing of the transmissionbandwidth, and introduction of ghost modes or'other types ofdistortions. A low loss wave permeable vacuum window of the block typedisposed within a hollow waveguide has beenfound to best satisfythecriteria of low transmission loss at high power levels in themulti-megawatt region While maintaining structural integrity during use.However, it has been determined that the block window is essentially anarrow band device and therefore means have to be provided to broadbandthe coupler means as well as to provide an optimum impedancetransformation between the source and the load points.

3,221,296 Patented Nov. 30, 1965 ice The present invention provides anovel solution in the form of a compact high frequency electromagneticwave transmissioncoupler having a pair of E-plane impedancediscontinuities within the coupler and a block window disposedtherebetween. The window is preferably a half wavelength long (thick) atthe center of the operating frequency of the pass band which it isdesired to transmit. To enhance the final match an inductive iris ispositioned within the coupler. The aforementioned coupler has been foundcapable of transmitting peak powers in excess of 6 megawatts and averagepowers in excess of 15 kilowatts without substantial reflection orintroduction of ghost modes within the desired pass band while effectingimpedance transformations between source and load points differing by,for example, 21 ratios and greater.

It is therefore an object of the present invention to provide animproved electron discharge device having novel electromagnetic wavetransmission coupler means therefore.

A feature of the present invention is the provision of a high frequencyelectron discharge device having electromagnetic wave transmissioncoupler means which include a wave permeable block window disposedwithin a waveguide with an E-plane impedance discontinuity disposed oneach side of said block window.

Another feature of the present invention is the device set forth in theaforementioned feature wherein said window is dimensioned to besubstantially n/2)\ long where substantially includes i1/12A as measuredat the center frequency of the pass band to be transmitted therethroughwhere n is any positive integer.

Another feature of the present invention is the provision of aninductive iris disposed within the coupler as defined in theaforementioned feature wherein said inductive iris is spaced from one ofsaid E-plane impedance discontinuities.

Another feature of the present invention is the provision of a highfrequency electron discharge device havig a broadband outputelectromagnetic wave energy transmission coupler comprising arectangular waveguide with a block window disposed therein and anE-plane discontinuity disposed on each side of said window, said E-plane discontinuities having impedance characteristics and displacementsfromvsaid window such that electromagnetic energy reflections withinsaid coupler are minimized while simultaneously broadbanding said windowfor said coupler design.

Another feature of the present invention is the provision of a highfrequency, broadband, high power, electromagnetic wave transmissioncoupler capable of maintaining a differential vacuum between therespective transmission ends thereof which coupler includes a wavepermeable block window disposed in vacuum sealed relation within awaveguide, said waveguide having an E- plane impedance discontinuitydisposed on each side of said Window, said E-plane discontinuitieshaving impedance characteristics and displacements from said window suchthat electromagnetic wave energy reflections within said coupler areminimized while simultaneously broadbanding said window for said couplerdesign.

Other features and advantages of the present invention will become moreapparent upon a perusal of the following specification taken inconjunction with the accompanying drawings wherein,

FIG. 1 is a perspective view of a high frequency high power travelingwave tube and electromagnetic wave energy transmission coupler meanstherefore.

FIG. 2 is an enlarged cross-sectional plan view of the transmissioncoupler taken along the lines 22 of FIG. 1 in the direction of thearrows.

FIG. 3 is a cross-sectional view of the transmission 3 coupler takenalong the lines 33 of FIG. 2 in the direction of the arrows.

FIG. 4 is a graphical portrayal of V.S.W.R. vs. frequency for atransmission coupler designed according to the teachings of the presentinvention.

FIG. 5 is a simplified version of a standard Smith Chart wherein amethod of designing the coupler of the present invention is outlined.

FIG. 6 is an enlarged cross-sectional view of a coupler designedaccording to the teachings of the present invention to cover a specificband of frequencies.

FIG. 7 is a schematic representation depicting the intermediate andfinal design stages of a coupler built according to the teachings of thepresent invention.

FIG. 8 is an illustrative graphical plot of aspect ratio vs. modefrequency for a block window such as utilized in the present invention.

FIG. 9 is a schematic representation of an alternative embodiment of thepresent invention.

FIG. 10 is a schematic representation of an alternative embodiment ofthe present invention.

FIG. 11 is a schematic representation of an alternative embodiment ofthe present invention.

Referring now to the drawings there is shown in FIG. 1 a high frequencyelectron discharge device 7 of the traveling wave type which isexemplary of the types of electron discharge devices which are enhancedthrough the utilization of the transmission coupler of the presentinvention. For the details of the traveling wave tube of the type suchas depicted in FIG. 1 see US. patent application Serial Number 56,415 byJ. A. Ruetz et al., filed September 16, 1960, and assigned to the sameassignee as the present invention. Other typical examples of highfrequency electron discharge devices wherein the transmission coupler ofthe present invention can advantageously be employed are such as, forexample, those depicted in U.S, Patents 2,915,670; 2,928,972; 2,963,616;3,028,519; and 3,096,462.

The traveling wave tube of the type depicted in FIG. 1 includes a beamforming and projecting portion or electron gun means 8, R.F. inputcoupler 9, slow wave electromagnetic interaction circuit portion 10, RF.energy transmission output coupler 11 and collector means 12 which areinterrelated in a vacuum sealed relationship.

In FIG. 2 an enlarged cross-sectional view of the transmission coupler11 is shown and includes rectangular waveguide 13 having the one endthereof 13 brazed in vacuum sealed relationship to a main body portionof the device envelope as shown. An electromagnetic wave permeable lowloss block window 14 is vacuum sealed within the waveguide by anysuitable ceramic to metal braze or the like. Spaced from said window oneach side thereof are E-plane impedance discontinuities 15, 16 as bestseen in FIG. 3. A set of inductive irises 17, 18 are positioned in thewaveguide 13 in spaced relation from the E-plane impedance discontinuity16 as shown. The other load or external end portion 19 of the coupler 11preferably terminates at a coupler flange 20 as shown. The waveguideportion 13 of the coupler 11 is characterized by having three sectionsA, B, C, respectively wherein each of said sections has different heightdimensions 12, and identical width dimensions a. Since the coupler 11 isdesigned to handle high powers all edges at the discontinuities, both Eand H plane types, are preferably rounded to minimize the possibility ofarcing.

The following relationships and definitions are presented to illustrateand define the physical and electrical parameters of a high powerbroadband coupler designed according to the teachings of the presentinvention.

Since free space wavelength 1 is defined as follows:

where c=velocity of light and f=frequency and the waveguide wavelength kfor a rectangular guide for the TE mode is defined as for air or vacuumand for window portion where e=dielectric constant of the medium(window) filling the guide 6 1 for air, and a=waveguide width, andrectangular waveguide impedance Z for the TE mode is defined by M; 1r I)Z 377 x 2 a where b=waveguide height. The following impedance parameterswere successfully matched at S Band for the coupler depicted in FIGS. 13having the physical and electrical parameters set forth in terms of A,1,; and A in FIG. 6 at a center frequency f of the passband to 3.1 kmc.with the following waveguide relationshps and the block window isalumina ceramic having a dielectric constant e=9.4

This design was found capable of handling average powers of about 15kilowatts and peak powers of above 6 megawatts without electricalbreakdown occurring within the guide while achieving good V.S.W.R.levels over a fairly wide passband as evidenced by the characteristicsdepicted in FIG. 4. It is seen upon examination of FIG. 4 that thecoupler design as set forth above achieved V.S.W.R.s of less than 1.15in the band from approximately 2.890 kmc. to 3.280 kmc. The moreimpressive features of this invention lie in the realization that theRF. coupler of the present invention is capable of handling high powerswithout appreciable loss in the passband through the combination of ablock window and E-plane impedance discontinuities which perform a duelfunction of simultaneously providing a smoooth substantiallyreflectionless impedance transformation between differential impedanceswhile broadbanding an otherwise narrow band block window disposedintermediate said E-plane impedance discontinuities. Quite obviously thepresent invention provides an extremely simple solution to the problemof transferring electromagnetic wave energy between points havingdifferential impedance and vacuum levels. It is also apparent that thepresent invention can transform energy between high and low impedancelevels as well as between low and high impedance levels as set forthhereinabove and hereinafter.

A design method such as set forth in the Smith Chart of FIG. 5 isadvantageously employed to provide a generalized design approach for themicrowave spectrum for a given set of differential impedance values whenusing the combination of a block window with E-plane impedancediscontinuities disposed on each side of said window. For an explanationof the utilization of the Smith Chart of the type depicted in FIG. 5 seeany standard microwave text. Sufiice it to say that once the combinationof block window and E-plane impedance discontinuities as set forth abovehas been chosen by the designer regardless of whether the choice of thiscombination was dictated by intuitive reasoning, system physicallimitations or for any other reason the following design approach can beutilized to set the electrical and physical parameters of the coupler ofthe present invention for a given set of differential impedance valuesbetween what can be termed the load and source points over which theelectromagnetic wave energy is to be transferred.

The block window will preferably be /z at the center .of the band offrequencies which it is desired to pass. However, it has been determinedthat the window can be n/2 wherein n is any positive integer and that itcan vary .in length +30% of any multiple of n/2A where n is any positiveinteger as determined at the center of the passband and still handlemulti-megawatt peak powers with good bandwidth and fairly smoothimpedance transformation between source and load. The dimensions of theoutput or load end 19 of the rectangular guide are predicated 'on thesystem load requirements which in the embodiment of FIG. 1-3 is astandard S-Band guide. The dimensions of the input or source end 13' ofthe rectangular guide are predicated to a certain extent on theimpedance present at the source which for purposes of explanation can bestated here as being the impedance value presented at the transmissionline output portion of the electron discharge device. i

The exact physical and electrical parameters chosen for the block windowand the waveguide parameters of the coupler can now be determined withthe aid of a Smith Chart once the basic combination of a block windowand a pair of E-plane discontinuities has been preselected. The firststep in the design procedure would be the selection of a suitablematerial for the block window. There are many commercially availablematerials having low loss and low dielectric constant parameters whichcould advantageously be employed such as, for example, fused quartz,beryllia ceramic, (BeO), alumina ceramic, single crystal sapphire, etc.For purposes of illustrating a specific embodiment alumina ceramic willbe employed. The dielectric constant of alumina cermic (A1 0 is 9.4. Inorder to obtain a good impedance match between the source and loadportions coupled with good bandwidth and to avoid the aforementionedghost modes in the passband of the window various combinations of windowlengths, widths, and heights or aspect ratios (A'/B) of the window canbe selected in conjunction with different combinations of E-planediscontinuities. The available combinations which would providereasonable solutions could conceivably approach astronomical numbers.Therefore, one can simplify the design by preselecting a window of agiven length (thickness) such as, for example, /zk and of a given aspectratio whichiin this case determines the waveguide width and heightdimensions for guide section B.

The selection of the window dimensions and thus the waveguide dimensionsof Section B are thus predicated on such factors as; the desiredmode-free bandwith; frequency range of interest such as S-Band, X-Band,etc.; lowest feasible electric field gradients for frequency range ofinterest; power handling capability of /2 Wavelength block window size.Reference is made to the following .article for a discussion of ghostmodes which is one of the aforementioned factors in determining theSection B waveguide dimensions as Well as the block window dimensions ofwidth, height and thickness: I.R.E. Transactions on Microwave Theory andTechniques, vol. M 'IT-8, No. 2,

March 1960, Resonant Modes in Waveguide Windows,

by M. P. Forrer and E. T. Iaynes.

It is possible to write an analytic set of equations, derived fromtransmission line and filter theory considerations, to describe a windowassembly in terms of the ceramic and any other arbitrary linear, passivematching elements.

Such an approach in general leads to a set of transcendental orotherwise cumbersome equations which often take longer tosolveanalytically for a specific design than to obtain similar resultsby judicious use of theSmith impedance plot.

, In the case of the block window, a mode search was first made for analumina block. geometry in the frequency sults.

as possible. F or an alumina block with relative dielectric constant of9.4 and cut to operate at 3.1 kmc., computation of the first order evenmodes showed that the bandwidth availablewas better than 14% using anaspect ratio of 2.63. Normal aspect ratio of WR 284 S-Band waveguide is2.12. The range of frequencies over which mode clearance wasprecalculated was from approximately 2.85 to 3.2-7'kmc. Ordinarily theblock would be cut to be age/2 at the center of the mode free band andthen broadbanded.

By terminating one end of the window and step with a non-reflective loadas shown in schematical FIG. 7, the Smith plot admittance function ofthe window was determined in the conventional way with slotted line asmeasured from an arbitrary but known plane, see FIG. 7, over thefrequency range of interest to obtain the desired impedance plot Z asshown in FIG. 5 by variation of the distance d, see FIG. 7, of thewindow to the E-plane discontinuity. A desired shape is obtained whenthe impedance function Z for a given d could be easily moved to circlethe origin by the addition of another E-plane discontinuity on theopposite side of the block. The Z function is appropriately shaped whenf (the center frequency of the passband) lies on or near the origin ofthe Smith plot and the bandedges of the passband are approximatelysymmetrical about either reactive branch of the circle on the Smith plotwhere the resistance or conductance is unity.

The point at which this admittance circle or loop goes through theorigin of the Smith plot is the frequency at which the window isresonant, or a half-wavelength long, the impedance plot Z is enlarged(more points are near the center) and thus broadbanded due to thecompensation of the first E-plane step.

Now it is seen that a properly chosen reference at plane X on the SmithChart and as shown in FIG. 7 would move the greater part of theadmittance circle into a path concentric with a point which later can bemoved to the origin of the Smith plot. Indeed, as we move to within 7kfrom the window the curve labeled as 2;; re-

Naturally the impedance loop or plot Z has opened up because of thedifferent rate of change between high and low frequency points when theyare referenced on a normalized Smith plot. The function (circle or loop)can now be brought down and to the right to circle the origin by theaddition of an appropriate step at this point. The reason for this shiftof loop Z to circle the origin is due to the change in impedance of thestep and the additional effect of the capacitive reactance of this step;in fact, plane X was chosen so that suitable compensation could be madethere.

After an appropriate step is made at plane X the function. is shifted asseen to plot Z All points are equal distance from the origin indicatinga constant V.S.W.R'. for a band of frequencies. A further slightimprovement of the match can now be made.

Since impedance points of constant V.S.W.R. may be closed by movingtoward the load (on the Smith plot high frequency points move fasterthan low frequency points because of smaller A it is excepted that theadmittance circle points around the origin can be found to cluster atsome reasonable distance from the window. Since a filter network wasanticipated in the beginning, this admittance cluster would again beexpected. A position was sought such that the cluster would fall on thepurely positive imaginary susceptance ordinate. This is found to occur2% from the window on the air side as was described previously.Obviously the above technique is applicable to a plurality of sets ofdifferential impedance values at Z Z Z with a block type of windowdisposed in the center waveguide section. The important point is that apair of E-plane impedance discontinuities can be utilized (to broadbanda block window) while simultaneously providing impedance matchingbetween differential impedance sections in order to obtain excellentsubstantially reflectionless electromagnetic energy transmission throughthe coupler. Trimmer inductive irises 17, 18 are advantageouslypositioned in the coupler to optimize the final match.

It is to be understood that the aforementioned design approach isequally applicable to any given set of load and source impedance valuesas well as being applicable to circular guides and windows.

Examination of FIG. 4 shows that for the parameters set forth in FIG. 3,a V.S.W.R. of less than 1.15 was achieved in the band from 2.89 kmc. to3.28 kmc.

FIGS. 9, 10 and 11 depict variants of the coupler depicted in FIGS. 1,2, 3 and 6 wherein more complex mechanical arrangements are depicted forproviding a pair of E-plane discontinuities on either side of a blockwindow. The embodiment of FIGS. 1, 2, 3 and 6 is obviously superior froma design standpoint since it is extremely simple to fabricate and thuseconomical, and also capable of handling higher powers without arcingdue to the presence of only one rounded edge at the E-planediscontinuities.

FIG. 9 depicts a coupler 42 having a pair of E-plane discontinuities 30,31 lying in a single plane on the one side of the block windows 32 and asingle E-plane discontinuity 33 on the opposite side.

FIG. 10 depicts a coupler having a pair of 34, 35 of E-planediscontinuities lying in a single plane on the one side of block window36 and another pair 37, 38 of E- plane discontinuities lying in a singleplane on the opposite side of the window 36.

FIG. 11 depicts a coupler 44 having an E-plane discontinuity 39 on theone side of block window 40 and an E-plane discontinuity 41 on theopposite side of the window with the E-plane discontinuities being onopposite broadwalls of the coupler.

In each of the above coupler designs depicted in FIGS. 9-11 the designtechniques set forth previously are advantageously employed to broadbandthe window and provide impedance matching characteristics for thedifferential impedance conditions. Quite obviously differentialimpedance conditions beyond the source and load points (input and outputportions of the coupler) may be prohibitively large in value such thatadequate broadbanding and matching is unobtainable with just a singleE-plane discontinuity on each side of the window as in the preferredembodiment or with the embodiments of FIGS. 911.

The present invention encompasses couplers with block windows andE-plane discontinuities having known impedance matching techniquesutilized prior to the source and load points of the coupler in order tobring the differential impedance levels within the limits of thebroadbanding and matching properties of a pair of E-planediscontinuities disposed on either side of a block window;

Furthermore, if ghost modes do not present a problem the presentinvention obviously is applicable to broadbanding a block windowregardless of the rationale which is used to determine the width andheight dimensions thereof. The aforementioned design techniques areobviously extendible to encompass coupler designs such as depicted inthe several embodiments of the present invention which have less thanoptimized bandwidths by selecting appropriate Z and Z plots in order toobtain a predetermined Z plot which is more or less governed by thesource requirements as mentioned previously. The 180 space rotatedembodiments depicted in FIGS. 9-11 are obviously applicable to circularguides as Well as rectangular.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electron discharge device including electron beamforming and projecting means, means for providing electromagneticinteraction between electromagnetic energy and an electron beam andelectromagnetic transmission coupler means coupled to said electrondischarge device, said coupler means including a hollow waveguide havinga low loss wave permeable block window disposed therein in vacuum sealedrelationship, the hollow waveguide portion of said coupler having an E-plane impedance discontinuity disposed on each side of said blockwindow, said coupler being further characterized by having waveguideportions on the outwardly directed ends of said E-plane impedancediscontinuities, said E-plane impedance discontinuities being spacedfrom said block window such that said block window is broadbanded, saidblock window having a length as measured along the transmission path ofsaid coupler which falls within the following range; substantially n/ZAwhere A is determined at the center frequency of the passband of thecoupler and n is any positive integer, said waveguide portions on theoutwardly directed ends of said E- plane impedance discontinuitieshaving differential impedance values, said E-plane impedancediscontinuities being inter-related with said block window such as tosimultaneously broadband said coupler passband while providing asubstantially rcflectionless impedance transformation between saiddifferential impedance values for electromagnetic energy within saidcoupler passband.

2. The device as defined in claim 1 wherein said block window has alength as measured along the transmission path of the coupler which isapproximately equal to n/IZA Where k is determined at the centerfrequency of the passband of the coupler and n is any positive integer.

3. The device as defined in claim 1 wherein said E- plane impedancediscontinuities are further characterized by their abrupt occurrence attwo spaced transverse planes through said hollow waveguide.

4. The device as defined in claim 1 wherein said E- plane impedancediscontinuities are restricted to a single side of said hollowwaveguide.

5. The device as defined in claim 1 wherein said block window and saidhollow waveguide are rectangular.

6. The device as defined in claim 1 including an inductive iris disposedin spaced relationship from one of said E-plane impedancediscontinuities.

7. The device as defined in claim 1 wherein said E- plane impedancediscontinuities are positioned on at least two space-rotated portions ofsaid hollow waveguide is spaced transverse planes through said hollowwaveguide to thereby form pairs of E-plane impedance discontinuities.

8. The device as defined in claim 1 wherein one of said E-planeimpedance discontinuities is positioned on at least two 180 spacerotated portions of said hollow waveguide in a transverse plane throughsaid hollow waveguide to thereby form a pair of E-plane impedancediscontinuities.

9. The device as defined in claim 1 wherein said E- plane impedancediscontinuities are positioned on 180 space rotated portions of saidhollow waveguide.

10. A high frequency electromagnetic coupler comprising a hollowrectangular waveguide having a low loss wave permeable block windowdisposed therein in vacuum sealed relationship, said block window havinga length as measured along the transmission path of said coupler whichfalls within the following range; substantially 11/21 where A isdetermined at the center frequency of the passband of the coupler and nis any positive integer, said hollow waveguide portion of said couplerhaving an E-plane impedance discontinuity disposed on each side of saidblock window, said coupler being further characterized by havingwaveguide portions 011 the outwardly directed ends of said E-planeimpedance discontinuities, said impedance discontinuities being spacedfrom said block Window such that said block window is broadbanded.

11. The coupler as defined in claim wherein said E- plane impedancediscontinuities are further characterized by their abrupt occurrence attwo spaced transverse planes through said hollow rectangular waveguide.

12. The coupler as defined in claim 10 wherein said E-plane impedancediscontinuities are restricted to a single side of said hollowrectangular waveguide.

13. The coupler as defined in claim 10 including an inductive irisdisposed in spaced relationship from one of said E-plane impedancediscontinuities.

14. The coupler as defined in claim 10 wherein said E-plane impedancediscontinuities are positioned on at least two 180 space rotatedportions of said hollow rectangular waveguide in spaced transverseplanes through said hollow rectangular waveguide to thereby form pairsof E-plane impedance discontinuities.

15. The coupler as defined in claim 10 wherein one of said E-planeimpedance discontinuities is positioned on at least two 180 spacerotated portions of said hollow rectangular waveguide in a transverseplane through said 10 hollow rectangular waveguide to thereby form apair of E-plane impedance discontinuities.

16. The device as defined in claim 10 wherein said E-plane impedancediscontinuities are positioned on 180 space rotated portions of saidhollow rectangular waveguide.

17. The device as defined in claim 10 wherein said waveguide portions onthe outwardly directed ends of said E-plane impedance discontinuitiesare characterized by having differential impedance values.

References Cited by the Examiner UNITED STATES PATENTS 2,576,186 11/1951Malter et a1. 333-98 2,698,421 12/1954 Kline et al. 33398 3,019,3991/1962 Lancioni et al 333- OTHER REFERENCES Moats, R. R.: Design ofBroadband Ceramic Coaxial Output Windows for Microwave Power Tubes. InThe Sylvania Technologist XI(3) pp. 86-90, July 1958.

HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

1. A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE INCLUDING ELECTRON BEAMFORMING AND PROJECTING MEANS, MEANS FOR PROVIDING ELECTROMAGNETICINTERACTION BETWEEN ELECTROMAGNETIC ENERGY AND AN ELECTRON BEAM ANDELECTROMAGNETIC TRANSMISSION COUPLER MEANS COUPLED TO SAID ELECTRONDISCHARGE DEVICE, SAID COUPLER MEANS INCLUDING A HOLLOW WAVEGUIDE HAVINGA LOW LOSS WAVE PERMEABLE BLOCK WINDOW DISPOSED THEREIN IN VACUUM SEALEDRELATIONSHIP, THE HOLLOW WAVEGUIDE PORTION OF SAID COUPLER HAVING ANEPLANE IMPEDANCE DISCONTINUITY DISPOSED ON EACH SIDE OF SAID BLOCKWINDOW, SAID COUPLER BEING FURTHER CHARACTERIZED BY HAVING WAVEGUIDEPORTIONS ON THE OUTWARDLY DIRECTED ENDS OF SAID E-PLANE IMPEDANCEDISCONTINUITIES, SAID E-PLANE IMPEDANCE DISCONTINUITIES BEING SPACEDFROM SAID BLOCK WINDOW SUCH THAT SAID BLOCK WINDOW IS BROADBANDED, SAIDBLOCK WINDOW HAVING A LENGTH AS MEASURED ALONG THE TRANSMISSION PATH OFSAID COUPLER WHICH FALLS WITHIN THE FOLLOWING RANGE; SUBSTANTIALLYN/2$GE WHERE $GE IS DETERMINED AT THE CENTER FREQUENCY OF THE PASSBANDOF THE COUPLER AND N IS ANY POSITIVE INTEGER, SAID WAVE-